From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 3AE2CC001DE for ; Mon, 31 Jul 2023 07:41:15 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229522AbjGaHlO (ORCPT ); Mon, 31 Jul 2023 03:41:14 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:49232 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230239AbjGaHlN (ORCPT ); Mon, 31 Jul 2023 03:41:13 -0400 Received: from dfw.source.kernel.org (dfw.source.kernel.org [IPv6:2604:1380:4641:c500::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id E569CDC; Mon, 31 Jul 2023 00:41:06 -0700 (PDT) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits)) (No client certificate requested) by dfw.source.kernel.org (Postfix) with ESMTPS id 1EE6D60F40; Mon, 31 Jul 2023 07:41:05 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id B0503C433C8; Mon, 31 Jul 2023 07:41:01 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1690789264; bh=N8xXDJhIqvl6gFtDtQlkTXSnFOUp5pK3mWMXr/11weY=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=Jr1uNHkLtZCsjH3HJ+2isbdKAE9neVgqV126e6gNrfJjAg0WF7Q3dB+6tFEGdlCnx 8f6rQDtv0yqInmPSvawCNmdPwJTKnalobyqngRtmbUDiPFx/3dMY/izQrZjl2vzTDL elJJFt0cmzhn8h+VSLa1mG542l6PyQssZ1JcYzqcH1asYCmBOzkfVNumZJXj10295J F4C7PgIZhNsiU9qKZ4++sQpWaxILisvqobilsNP3lowfG6nTnjQAQ8m46glh5e5BvI w/1fOQ6+OKAleTmM2bQAjFs0SEiA1eaTzC1Ezhm0lwyp+rOj7RJOCRZ88JR0lFsNBc tpjP60mI/qIYA== Date: Mon, 31 Jul 2023 09:40:58 +0200 From: Christian Brauner To: Dave Chinner Cc: Pavel Begunkov , Hao Xu , djwong@kernel.org, Jens Axboe , io-uring@vger.kernel.org, Dominique Martinet , Alexander Viro , Stefan Roesch , Clay Harris , linux-fsdevel@vger.kernel.org, Wanpeng Li , josef@toxicpanda.com Subject: Re: [PATCH 3/5] io_uring: add support for getdents Message-ID: <20230731-kooperativ-akquirieren-fd700d697cfd@brauner> References: <20230718132112.461218-1-hao.xu@linux.dev> <20230718132112.461218-4-hao.xu@linux.dev> <20230726-leinen-basisarbeit-13ae322690ff@brauner> <20230727-salbe-kurvigen-31b410c07bb9@brauner> <2785f009-2ebb-028d-8250-d5f3a30510f0@gmail.com> <20230727-westen-geldnot-63435c2f65ad@brauner> <77feb96e-adf7-56f2-dac5-ca5b075afa83@gmail.com> <20230727-daran-abtun-4bc755f668ad@brauner> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: io-uring@vger.kernel.org On Mon, Jul 31, 2023 at 11:58:50AM +1000, Dave Chinner wrote: > On Thu, Jul 27, 2023 at 06:28:52PM +0200, Christian Brauner wrote: > > On Thu, Jul 27, 2023 at 05:17:30PM +0100, Pavel Begunkov wrote: > > > On 7/27/23 16:52, Christian Brauner wrote: > > > > On Thu, Jul 27, 2023 at 04:12:12PM +0100, Pavel Begunkov wrote: > > > > It would also solve it for writes which is what my kiocb_modified() > > > > comment was about. So right now you have: > > > > > > Great, I assumed there are stricter requirements for mtime not > > > transiently failing. > > > > But I mean then wouldn't this already be a problem today? > > kiocb_modified() can error out with EAGAIN today: > > > > ret = inode_needs_update_time(inode, &now); > > if (ret <= 0) > > return ret; > > if (flags & IOCB_NOWAIT) > > return -EAGAIN; > > > > return __file_update_time(file, &now, ret); > > > > the thing is that it doesn't matter for ->write_iter() - for xfs at > > least - because xfs does it as part of preparatory checks before > > actually doing any real work. The problem happens when you do actual > > work and afterwards call kiocb_modified(). That's why I think (2) is > > preferable. > > This has nothing to do with what "XFS does". It's actually an > IOCB_NOWAIT API design constraint. > > That is, IOCB_NOWAIT means "complete the whole operation without > blocking or return -EAGAIN having done nothing". If we have to do > something that might block (like a timestamp update) then we need to > punt the entire operation before anything has been modified. This > requires all the "do we need to modify this" checks to be done up > front before we start modifying anything. > > So while it looks like this might be "an XFS thing", that's because > XFS tends to be the first filesystem that most io_uring NOWAIT > functionality is implemented on. IOWs, what you see is XFS is doing > things the way IOCB_NOWAIT requires to be done. i.e. it's a > demonstration of how nonblocking filesystem modification operations > need to be run, not an "XFS thing"... Yes, I'm aware. I was trying to pay xfs a compliment for that but somehow that didn't come through. > > > > > I would prefer 2) which seems cleaner to me. But I might miss why this > > > > won't work. So input needed/wanted. > > > > > > Maybe I didn't fully grasp the (2) idea > > > > > > 2.1: all read_iter, write_iter, etc. callbacks should do file_accessed() > > > before doing IO, which sounds like a good option if everyone agrees with > > > that. Taking a look at direct block io, it's already like this. > > > > Yes, that's what I'm talking about. I'm asking whether that's ok for xfs > > maintainers basically. i_op->write_iter() already works like that since > > the dawn of time but i_op->read_iter doesn't and I'm proposing to make > > it work like that and wondering if there's any issues I'm unaware of. > > XFS already calls file_accessed() in the DIO read path before the > read gets issued. I don't see any problem with lifting it to before > the copy-out loop in filemap_read() because it is run regardless of > whether any data is read or any error occurred. Hence it just > doesn't look like it matters if it is run before or after the > copy-out loop to me.... Great.